Pyrolytic Carbon Implants With Porous Fixation Component And Methods Of Making The Same

ABSTRACT

An orthopedic implant including an articulation portion having a pyrolytic carbon bearing surface and a porous bone on- or in-growth structure, and methods of making the same.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application Ser. No. 61/387,678, filed Sep. 29, 2010, which is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to prosthetic orthopedic implants, and more particularly to prosthetic orthopedic implants for use in bone joints and methods of making the same. Even more particularly, the present disclosure relates to prosthetic orthopedic implants that include a pyrolytic carbon bearing or articulating surface and a porous bone fixation structure.

BACKGROUND

Pyrolytic carbon has gained a lot of interest over the past few years as a bearing material in orthopedic applications. The material shows excellent wear characteristics, a modulus of elasticity similar to bone, and high strength. Pyrolytic carbon implants are commonly made by depositing a layer of pyrolytic carbon on a graphite substrate or core. Typically, pyrolytic carbon implants included a solid or non-porous bone fixation portion that is implanted into the bone and relies on a press-fit interference with surrounding bone tissue for fixation of the implant to the bone.

Bone on-growth or in-growth porous structures, such as porous tantalum and titanium structures, are sometimes used in orthopedic implants as the bone fixation component of the implant. Such porous structures are implanted into the bone and are designed to foster osseointegration. Osseointegration is the integration of living bone tissue within a man-made material. The porous structure and the bone material become intermingled as the bone grows into the pores. This intermingling of the bone tissue with the porous structure can enhance fixation between the orthopedic implant and the bone tissue. Because of the difficulties of bonding porous on-growth and in-growth structures to pyrolytic carbon and graphite surfaces, pyrolytic carbon implants have not included such porous fixation surfaces.

SUMMARY

In one aspect, the present disclosure is directed to an orthopedic implant including an articulation portion having a pyrolytic carbon bearing surface. The implant also includes a bone fixation portion extending from the articulation portion and having a porous structure configured for bone on-growth or bone in-growth.

In another aspect, a method of forming an orthopedic implant. The method includes providing a member having a first portion and a porous second portion. A layer of pyrolytic carbon is applied to a surface of the first portion and a metal is applied to the porous second portion.

In yet a further aspect, a method of forming an orthopedic implant that includes applying a layer of pyrolytic carbon to a first surface of a substrate and placing an interlayer comprising a metal between a second surface of the substrate and a porous metal structure. The porous metal layer, substrate and the interlayer are bonded together.

In yet another aspect, a method of forming an orthopedic implant including applying a layer of pyrolytic carbon to a first surface of a substrate and applying a metal interlayer to a second surface of the substrate. A porous metal structure is placed in contact with the metal interlayer, and a second outer layer of metal is applied to the substrate, interlayer and porous metal structure to bond the porous metal structure to the substrate.

In yet a further aspect, a method of forming an orthopedic implant includes applying a layer of pyrolytic carbon to a first surface of a substrate and applying an interlayer comprised of a metal to a second surface of the substrate. A metal sheet is then placed between the interlayer and a porous metal structure, and heat and pressure are applied to bond the metal structure, metal sheet and interlayer together.

BRIEF DESCRIPTION OF THE FIGURES

In the course of this description, reference will be made to the accompanying drawings, wherein:

FIG. 1 is a perspective view of one embodiment of an implant of the present disclosure;

FIG. 2 is a cross-sectional view of the implant of FIG. 1;

FIG. 3 is a cross-sectional view of another embodiment of an implant of the present disclosure;

FIG. 4 is an elevation view of yet another embodiment of an implant of the present disclosure;

FIG. 5 is a cross-sectional view of the implant of FIG. 4;

FIG. 6 is a cross-sectional view of another embodiment of an implant of the present disclosure;

FIG. 7 is a cross-sectional view of still yet another embodiment of an implant of the present disclosure;

FIG. 8 is a cross-sectional view of another embodiment of an implant of the present disclosure;

FIG. 9 a is a schematic illustration of one embodiment of a method of making an implant of the present disclosure;

FIG. 9 b is a flow-chart showing the method illustrated in FIG. 7 a;

FIG. 10 a is a schematic illustration of another embodiment of a method of making an implant of the present disclosure;

FIG. 10 b is a flow-chart showing the method illustrated in FIG. 8 a;

FIG. 11 a is a schematic illustration of yet another embodiment of a method of making an implant of the present disclosure;

FIG. 11 b is a flow-chart showing the method illustrated in FIG. 9 a;

FIG. 12 is a flow-chart of one embodiment of a method of making an implant of the present disclosure; and

FIG. 13 is a flow-chat of another embodiment of a method of making an implant of the present disclosure.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosed herein; however, it will be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner.

Generally, the prosthetic implants disclosed herein include an articulation portion having a pyrolytic carbon bearing or articulating surface and a porous bone in-growth or on-growth fixation structure or portion which is combined or otherwise associated with the articulation portion. Pyrolytic carbon is a brittle material that is biocompatible with bone and cartilage. It has good wear and strength properties and has been found to be a good bearing or articulating material for joint repair and replacement applications. The bearing surface of implants may articulate against, for example, natural body tissues, such as bone, or may articulate against a surface of an adjacent prosthetic component. Such implants are particularly useful in bone joint repair and replacement and may be used to treat or repair defects in, for example, the knee, hip, shoulder, fingers, elbow, toes or ankle. However, it will be appreciated that the use of such implants are not limited to joint repair or in connection with the joints specifically identified.

Referring to FIGS. 1 and 2, implant 10 a includes a first portion or articulation portion 12 a associated with a second portion or bone fixation portion 14 a. In the illustrated embodiment, the bone fixation portion 14 a is shaped to be received into or implanted into a section of bone at the location of a joint and includes a porous bone in-growth or on-growth structure or region. The articulation portion 12 a further includes a bearing surface 16 a that is comprised of pyrolytic carbon and that functions as an articulating or bearing surface for the implant 10 a. In the illustrated embodiment, the bearing surface 16 a forms an outer layer or cover of the articulation portion 12 a, and more specifically entirely covers an underlying body or substrate 24 a (see FIG. 2). However, it will be appreciated that the bearing surface 16 a may be sized to only cover a portion or multiple portions of the substrate 24 a depending on the desired articulation points of the implant. Alternatively, the entire articulation portion 12 a could be formed of pyrolytic carbon.

In the embodiment illustrated in FIGS. 1 and 2 and other figures contained herein, the articulation portion 12 a is hemisphericaly shaped or ball-shaped. In this configuration, the articulation portion 12 a may function, for example, as the articulating head or ball of a ball and socket joint commonly found in hip or shoulder. The articulation portion 12 a of this and other embodiments described herein may be, however, designed for other joint functions, used in other types of joints, or even used for other orthopedic applications. Accordingly, the articulation portion 12 a may take on any variety of suitable sizes and regular and irregular geometric shapes, depending on the application. For example, the articulation portion may be cubical, cylindrical, cup-shaped, etc. In addition, depending on the desired application, the bearing surface 16 a may take on any variety of configurations, for example, concave.

The second or bone fixation portion 14 a preferably includes a porous structure or region 26 a in order to allow for bone in-growth or on-growth. In one embodiment, the bone fixation portion 14 a may be made entirely or partially from a porous material or made to contain pores and more specifically surface pores 20 a. Further, the bone fixation portion 14 a includes a projection or stem element 22 a that is sized and shaped to be implanted into bone. In the illustrated embodiment, the stem element 22 a has a polygonal cross-section and, more particularly a hexagonal cross-section. In other embodiments, the stem element 22 a may have other polygonal shapes or may be cylindrical, spherical, conical, or any other suitable configuration. In further embodiments, multiple projections or stem elements 22 a may be incorporated to assist in limiting implant rotation or to provide different bone fixation arrangements.

When implanted within bone, the porous structure or region 26 a of the bone fixation portion 14 a and in particular the stem element 22 a is receptive to bone cell and tissue on- and/or in-growth which enhances fixation of the implant 10 a to the bone. The porous region 26 a of the bone fixation portion 14 a and the porous regions of the bone fixation portions of other embodiments described herein may have a pore size, pore interconnectivity, and/or other features that facilitate bone tissue on- and/or in-growth into the pores, as known in the art. Preferably, the bone fixation portion 14 a is formed entirely from a highly porous material or a material adapted to be porous that may have a porosity as low as about 55, 65, or 75 percent by volume or as high as about 80, 85, or 90 percent by volume. However, it will be appreciated that the bone fixation portion 14 a may not be entirely constructed of a porous material but includes region(s) comprised of porous materials positioned thereon.

Referring to FIG. 2, in this embodiment, the implant 10 a has a core 18 a that includes the body or substrate 24 a of the articulation portion 12 a and the porous section or region 26 a of the bone fixation portion 14 a. In one embodiment, the core 18 a and consequently the substrate 24 a and porous region 26 a may be constructed out of a single material, for example, carbon, and more particularly, a dense, isotropic graphite. As such, the substrate 24 a and the porous stem element 22 a may be of a one-piece or unitary body or construction.

In order to enhance the visibility of the implant or portions thereof under fluoroscopy or x-ray imaging, the carbon may be doped with or otherwise include any suitable radiopacifiers, such as tungsten, zirconia or barium sulphate. In the embodiment illustrated in FIG. 2, the substrate 24 a includes an exterior surface 28 a that has pyrolytic carbon layer 30 a positioned at least partially thereon. The pyrolytic carbon layer 30 a helps form the bearing surface 16 a of articulation portion 12 a. It shall be appreciated that core 18 a also may be constructed out of any other suitable material that can have pyrolytic carbon applied thereto and is suitable for use in orthopedic applications.

The pyrolytic carbon layer 30 a may be applied to the substrate 18 a by any suitable method known in the art. For example, the pyrolytic carbon layer 30 a may be applied by chemical vapor deposition (CVD) or physical vapor deposition (PVD). In the embodiment shown in FIG. 2 and other embodiments described herein, the pyrolytic carbon layer 30 a has a uniform thickness. The thickness of the pyrolytic carbon layer 30 a, however, may vary to accommodate particular applications of the implant. Preferably, the pyrolytic carbon layer 30 a has a thickness of at least about 50 μm. In other embodiments, the pyrolytic carbon layer 30 a has a thickness of at least about 200 μm, 300 μm, 400 μm or 500 μm. In other embodiments, the pyrolytic carbon layer is between about 500 μm and 1000 μm.

Referring back to bone fixation portion 14 a, in this embodiment, the bone fixation portion 14 a comprises porous region 26 a of the core 18 a. As explained in more detail below, porous region 26 a of core 18 a may be formed by drilling or machining holes or pores 20 a or a matrix of holes or pores into and/or through the porous region 26 a. The resultant holes or pores 20 a of porous region 26 a may then be infiltrated and coated with a coating, such as a metal coating, to promote bone in-growth or on-growth, as described in more detail below. In one embodiment, the pores 20 a pass through the entire bone fixation portion 14 a. In other embodiments, the pores 20 a are created to a porous region that extends between about 500 um and 4000 um and preferably between about 1000 um and 2000 um from the outer surface and into the bone fixation portion 14 a. Alternatively, as discussed below with respect to FIGS. 7 and 8, the porous region 26 a could be constructed out of a material with the desired porosity and attached or applied to the core.

A schematic illustration and flowchart of one embodiment of a method of making the implant 10 a illustrated in FIGS. 1 and 2 are shown in FIGS. 9 a and 9 b, respectively. It is understood that the steps of the method may be carried out in any suitable order which results in an implant fit for its desired orthopedic use. In one step, a block of carbon 32 a, preferably a dense, isotropic graphite, is machined or otherwise processed into a desired shape to form the core 18 a of implant 10 a. In the embodiment shown, the block 32 a is machined into a core 18 a having a substrate 24 a and a bone fixation portion 14 a. The substrate 24 a at least partially forms the articulation portion 12 a. Holes or pores 20 a or a matrix of holes or pores are then created in the bone fixation portion 14 a of the core 18 a, resulting in a porous region 26 a of bone fixation portion 14 a. In one embodiment, the bone fixation portion 14 a is drilled or otherwise machined to create holes 20 a in porous region 26 a.

In another step, the bone fixation portion 14 a is masked or otherwise protected or covered leaving substrate 24 a of core 18 a exposed and a pyrolytic carbon layer 30 a is applied to the outer surface 28 a of substrate 24 a. The pyrolytic carbon layer 30 a may be applied by any suitable process. In one embodiment, the pyrolytic carbon layer 30 a is applied by CVD. In yet another step, the articulation portion 12 a/substrate 24 a is masked or otherwise protected and covered leaving the bone fixation portion 14 a and more particularly the porous region 26 a exposed and a coating is applied to at least a portion of the porous region 26 a so that the coating infiltrates the holes 20 a and coats the porous regions 26 a of second portion 14 a. In one embodiment, the coating is a metal such as but not limited to, tantalum, titanium, niobium, alloys of the same or any other suitable metal or alloy. Further, the metal may be applied to the porous regions 26 a by, for example, CVD, PVD or any other suitable process. Other examples of coatings include bone on-growth or in-growth coatings such as hydroxyapatite or forms of calcium phosphate.

The resulting implant 10 a includes a articulation or first portion 12 a including a pyrolytic carbon bearing surface 16 a and second or bone fixation portion 14 a having a porous structure or region 26 a that is suitable for bone cell and tissue on- and/or in-growth.

FIG. 3 illustrates another embodiment of an implant 10 b of the present disclosure which includes an articulation or first portion 12 b and a second or bone fixation portion 14 b with a porous region 26 b. Similar to the previous embodiment, the articulation portion 12 b includes a body or substrate 24 b having a pyrolytic carbon layer 30 b thereon that forms the bearing surface 16 b. The substrate 24 b may be made of any material or combination of materials suitable for having pyrolytic carbon applied thereto and in one embodiment the substrate 24 b is carbon, preferably a dense, isotropic graphite. Additionally, in order to enhance the visibility of the implant or portions thereof under fluoroscopy or x-ray imaging, the carbon may be doped with or otherwise include any suitable radiopacifiers, such as tungsten, zirconia and barium sulphate.

In this embodiment, the bone fixation portion 14 b comprises a porous structure preferably constructed out of metal. The bone fixation portion 14 b is separately formed and is not unitary with the substrate 24 b. The bone fixation portion 14 b may be made of any suitable porous bone on-or in-growth metal structure known in the art. For example, the bone fixation portion 14 b may be made of Trabecular Metal®, generally available from Zimmer, Inc. of Warsaw, Ind. Such material may be formed from a reticulated vitreous carbon foam substrate which is infiltrated and coated with a metal, such as tantalum, titanium, niobium, alloys of the same or any other suitable metal or alloy, by a CVD process in the manner disclosed in U.S. Pat. No. 5,282,861. The porous metal structure may have a pore size, pore interconnectivity, and/or other features that facilitate bone tissue on-and/or in growth.

As described in more detail below, the bone fixation portion 14 b is bonded or otherwise attached to the substrate 24 b of the articulation portion 12 b by a metal interlayer 34 b and/or a metal outer layer 36 b. The metal interlayer 34 b may be a layer of metal deposited or otherwise placed on a surface of substrate 24 b or may be a sheet or foil positioned between substrate 24 b and bone fixation portion 14 b. Preferably, metal interlayer 34 b and metal outer layer 36 b are constructed out of the same metal or alloy as that of the bone fixation portion 14. It should be noted that the thicknesses of metal interlayer 34 b and metal outer layer 36 b are not drawn to scale in the figures, but have been exaggerated for illustrative purposes. Such interlayer 34 b may have a thickness of between about 100 um and about 1 mm, and more preferably between about 400 um and about 600 um. The outer layer 36 b may have a thickness of between about 50 um and about 400 um, and more preferably between about 150 um and about 250 um. However, it will be appreciated that the thicknesses may be altered in order to obtain the desired implant properties.

A schematic illustration and flowchart showing one embodiment of a method of making implant 10 b are shown in FIGS. 10 a and 10 b, respectively. It is understood that the steps of the method may be performed in any order that produces an implant suitable for use in orthopedic applications. A block of carbon 32 b, preferably a dense, isotropic or fiber reinforced graphite, is machined or otherwise processed to form the substrate 24 b of articulation portion 12 b of the implant 10 b. In order to form bearing surface 16 b, a pyrolytic carbon layer 30 b is applied to an outer surface 28 b of substrate 24 b by any suitable method known in the art. For example, the pyrolytic carbon layer may be applied by CVD.

An interlayer 34 b, preferably metallic and more specifically, a tantalum or titanium interlayer, is applied to outer surface 38 b of the substrate 24 b. The metal interlayer 34 b may be applied by any suitable method known in the art, such as CVD or PVD. Further, the metal interlayer 34 b may be formed of a metal foil or sheet. Undercuts, holes and/or other surface deviations may be located or formed in substrate 24 b, and particularly in outer surface 38 b, so that when the metal interlayer 34 b is applied to outer surface 38 b, the metal enters and engages the undercuts, holes, etc. to form a mechanical interlock between the interlayer 34 b and substrate 24 b.

The bone fixation portion 14 b, which is comprised of a porous metal structure and preferably a porous tantalum structure, is placed against the metal interlayer 34 b. A metal outer layer 36 b, preferably a tantalum metal outer layer, is applied to the bone fixation portion 14 b, the metal interlayer 34 b, and substrate 24 b/articulation portion 12 b. Again, the substrate 24 b may include undercuts, holes or other deviation so that when outer layer 36 b is applied, the metal may engage and enter such undercuts, holes or other deviations in the surface to create a mechanical interlock. Preferably, but not necessarily, the interlayer 34 b, outer layer 36 b and bone fixation portion 14 b are all constructed of the same metal. After the outer layer 36 b has been applied, the metal interlayer 34 b, metal outer layer 36 b and bone fixation portion 14 b are subjected to elevated temperatures to bond the bone fixation portion 14 b to substrate 24 b and form the implant 10 b.

FIGS. 4 and 5 illustrate another embodiment of an implant 10 c of the present disclosure. Similar to the other embodiments, the implant 10 c includes a articulation or first portion 12 c and a bone fixation or second portion 14 c. Referring to FIG. 5, the articulation portion 12 c includes a body or substrate 24 c. The substrate 24 c includes a surface 28 c having a pyrolytic carbon layer 30 c positioned thereon. The substrate 24 c may be made of any material or combination of materials suitable for having pyrolytic carbon applied thereto and in one embodiment the substrate 24 c is carbon, preferably a dense, isotropic or fiber reinforced graphite. Additionally, in order to enhance the visibility of the implant or portions thereof under fluoroscopy or x-ray imaging, the carbon may be doped with or otherwise include any suitable radiopacifiers, such as tungsten, zirconia or barium sulphate.

Bone fixation portion 14 c may be made of any suitable porous bone on-or in-growth metal structure described herein or known in the art. Alternatively, the bone fixation portion could be constructed of a material that could be made porous through any method known in the art. The porous bone fixation portion 14 c is bonded to the substrate 24 c using interlayer 40 c. Interlayer 40 c is preferably a metal that is readily soluble with the metal of the porous stem 14 c. As explained in more detail below, interlayer 40 c may be applied to surface 38 c of the substrate 24 c by any suitable deposition process, such as CVD or PVD. Undercuts, holes and/or other surface deviations may be located in substrate 24 b, and particularly in surface 38 c, so that when the metal interlayer 40 c is applied to surface 38 c, the metal enters and engages the undercuts, holes, etc. to form a mechanical interlock between the metal interlayer 40 c and substrate 24 c. In another embodiment, the interlayer 40 c may be a metal sheet or foil.

In a further embodiment, as shown in FIG. 6, the implant 10 c may include both a deposited interlayer 40 c and a thin interlayer such as a metal foil or sheet 42 c located between bone fixation portion 14 c and substrate 24 c to assist in the bonding process. It should be noted that the thicknesses of metal interlayer 40 c and metal foil 42 c are not drawn to scale in the figures, but have been exaggerated for illustrative purposes. The interlayer 40 c may have a thickness of between about 100 um and about 1000 um, and more preferably between about 400 um and about 600 um. The foil sheet 42 c may have a thickness of between about 100 um and about 1000 um, and more preferably between about 400 um and about 600 um.

A schematic illustration and flowchart showing one embodiment of a method of making the implants 10 c illustrated in FIGS. 5 and 6 are shown in FIGS. 11 a and 11 b, respectively. The steps of the method described herein may be performed in any order that produces an implant suitable for use in orthopedic applications. A block of carbon 32 c, preferably a dense, isotropic graphite, is machined or otherwise processed to form the substrate 24 c of articulation portion 12 c of the implant. A pyrolytic carbon layer 30 c is applied to an outer surface 28 c of the substrate 24 c. A metal interlayer 40 c, preferably comprised of a metal that is readily soluble with the metal of the porous metal second portion 14 c, is applied to surface 38 c of substrate 24 c. In one embodiment, the metal interlayer is comprised of titanium. The metal interlayer 40 c may be applied by any suitable process know in the art, such as CVD. Undercuts, holes or other surface deviations may be located in the substrate 24 c, and in particular surface 38 c, so that when the metal interlayer 40 c is applied to the substrate 24 c, the metal enters and engages the undercuts, holes, etc. to form a mechanical interlock between the metal interlayer 40 c and substrate 24 c. In another embodiment, interlayer 40 c is a metal foil or sheet.

A bone fixation portion 14 c comprised of a porous metal structure, such as any of the porous metal structures described herein or known in the art, is placed against the metal interlayer 40 c to form an assembly. In one embodiment, one of the porous bone fixation portion 14 c and the interlayer 40 c is comprised of tantalum and the other one is comprised of titanium. Optionally, an interlayer such as a metal foil or sheet (not shown) may be placed between the porous metal bone fixation portion 14 c and a deposited metal interlayer 34 c so that the implant includes both a deposited metal interlayer 40 c and a metal foil or sheet. In one embodiment the metal foil or sheet is constructed out of the same metal as the interlayer 34 c.

Heat and pressure are applied to the assembly for a period of time sufficient to induce solid state diffusion between the interlayer 40 c and porous metal bone fixation portion 14 c, and, if used, the metal foil or sheet. As is known to those skilled in the art, solid-state diffusion is the movement and transport of atoms in solid phases. Solid-state diffusion bonding forms a joint through the formation of bonds at an atomic level due to transport of atoms between two or more metal surfaces. Heat and pressure may be supplied to the assembly by a variety of methods known in the art. For example, the assembly may be heated electrically, radiantly, optically, by induction, by combustion, by microwave, or any other suitable means known in the art. Pressure may be applied mechanically by clamping the assembly together prior to insertion of the assembly into a furnace, or pressure may be applied via a hot pressing system capable of applying pressure once the assembly reaches a target temperature, as is known in the art. Furthermore, hot pressing may include hot isostatic pressing, also known in the art. In one embodiment, the assembly is clamped and heated to at least about 940° C. for 4 hours in a vacuum or in another sub-atmospheric pressure of an inert atmosphere.

Preferably, the clamped assembly is heated to less than the melting temperature of the components. The time required to achieve bonding may be as little as less than 1 hour and as long as about 48 hours, and will depend on the metals involved, the temperatures, atmosphere and the pressures applied. After the diffusion process has been completed, the implant is formed.

Yet another embodiment of an implant 10 d of the present disclosure is illustrated in FIG. 7. Implant 10 d includes a core 18 d that defines a substrate 24 d for an articulation portion 12 d and a substrate 25 d for a bone fixation portion 14 d. Similar to other embodiments disclosed herein, the substrate 24 d of the articulation portion 12 d has a pyrolytic carbon layer 30 d thereon that forms the bearing surface 16 d. The core 18 d may be made of any material or combination of materials suitable for having pyrolytic carbon applied thereto and in one embodiment the substrate 24 d is carbon, preferably a dense, isotropic graphite. Additionally, in order to enhance the visibility of the implant or portions thereof under fluoroscopy or x-ray imaging, the carbon may be doped with or otherwise include any suitable radiopacifiers, such as tungsten.

The bone fixation portion 14 d further includes a porous exterior layer 46 d overlaying at least a portion of substrate 25 d of core 18 d to form porous region 26 d. The exterior layer 46 d may be made of any suitable porous bone on- or in-growth material known in the art. For example, the exterior layer 46 d may be made of metal structure such as but not limited to titanium or tantalum. However, it will be appreciated that other materials may be used depending upon the desired characteristics of the implant. The porous region 26 d may have a thickness, pore size, a pore interconnectivity, and/or other features that facilitate bone tissue on-and/or in growth. In one embodiment, the exterior layer 46 d/porous region 26 d may have a thickness of between about 5 μm and about 300 μm. In order to facilitate the bonding of the exterior layer 46 d to the substrate 24 d, the bone fixation portion 14 d may include an intermediate layer 44 d. In the embodiment illustrated in FIG. 7, the intermediate layer 44 d is formed from a metal such as titanium that is applied via CVD or PVD onto the substrate 25 d of core 18 d. The intermediate layer 44 d may have a thickness of up to about 1 mm.

FIG. 12 is a flowchart showing one embodiment of a method of making the implant 10 d illustrated in FIG. 7. The steps of the method described herein may be performed in any order that produces an implant illustrated in FIG. 7. In one step, a block of carbon, preferably a dense, isotropic graphite, is machined or otherwise processed to form core 18 d with substrate 24 d and substrate 25 d. In another step, a pyrolytic carbon layer 30 d is applied to the outer surface 28 d of substrate 24 d of the articulation portion 12 d. An intermediate layer 44 d, preferably comprised of a metal that can adhere to the graphite substrate 24 e is applied, preferably via CVD or PVD, to an outer surface of the substrate 25 d of the bone fixation portion 14 d. The exterior porous layer 46 d is applied to the intermediate layer 44 d, preferably via plasma spraying. However, it will be appreciated that any other suitable method of attaching the exterior layer 46 d to the intermediate layer 44 d or directly to the substrate 25 d if the intermediate layer is omitted may be used. The bearing surface 16 d of the pyrolytic carbon layer 30 d may be polished or otherwise treated or conditioned in order to obtain a generally smooth articulating surface.

Turning to FIG. 8, implant 10 e is another embodiment of an orthopedic device of the present disclosure and is similar to the other implants disclosed herein. Implant 10 e includes a metallic core 18 d, such as but not limited to titanium or tungsten, that partially defines an articulation portion 12 e and bone fixation portion 14 e. The articulation portion 12 e has a pyrolytic carbon layer 30 e thereon that forms the bearing surface 16 e. An intermediate layer 19 e is positioned between the pyrolytic carbon layer 30 e and the core 18. The intermediate layer 19 e is preferably constructed out of a material, such as carbon, preferably a dense, isotropic graphite, that can bond or otherwise adhere to the metal core 18 e and pyrolytic carbon layer 30 e. The core 18 e also forms the interior portion of the bone fixation portion 14 e and is at least partially surrounded by a porous exterior layer 46 e that forms the porous region 26 e. In the illustrated embodiment, the exterior layer 46 e is made of a metal such as but not limited to porous titanium or tantalum metal structures. In one embodiment, the exterior layer 46 e is Trabecular Metal®, generally available from Zimmer, Inc. of Warsaw, Ind. It will be appreciated, however, that other materials for the exterior layer 46 e may be used depending upon the desired characteristics of the implant. The exterior layer 46 e/porous region 26 e preferably have a thickness, pore size, a pore continuity, and/or other features that facilitate bone tissue on-and/or in growth.

FIG. 13 is a flowchart showing one embodiment of a method of making the implant 10 e illustrated in FIG. 8. The steps of the method described herein may be performed in any order that produces an implant illustrated in FIG. 8. In one step, the metallic core is formed to the desired shape using a metal such as but not limited to titanium or tungsten. In another step, a block of carbon, preferably a dense, isotropic graphite, is machined or otherwise processed to form the intermediate layer 19 e. The core 18 e and intermediate layer 19 e are positioned adjacent one another. Heat and pressure are applied to the assembly for a period of time sufficient to induce solid state diffusion between the core 18 e and intermediate layer 19 e. In another step, a pyrolytic carbon layer 30 e is applied to the outer surface 28 e of the intermediate layer 19 e. The bearing surface 16 e of the pyrolytic carbon layer 30 e may be polished or otherwise treated or conditioned in order to obtain a generally smooth articulating surface. An exterior layer 46 e is applied to the core 18 e of the bone fixation portion 14 e to form the porous region 26 e. The exterior layer 46 e is preferably comprised of a metal that can adhere to the material of the core 18 e. in one embodiment, the exterior layer 46 e comprised of a metal such as titanium is applied to the core 18 e, preferably via plasma spaying. Alternatively, the exterior layer 46 e may be comprised of a porous tantalum metal structure such as Trabecular Metal®, generally available from Zimmer, Inc. of Warsaw, Ind. In this embodiment, the metal exterior layer 46 e may be positioned adjacent the core 18 e. Heat and pressure are applied to the assembly for a period of time sufficient to induce solid state diffusion between the metal exterior layer 46 e and the core 18 e. It will be appreciated that bonding of the core 18 e and intermediate layer 19 e to one another and the exterior layer 46 e to the core 18 e could be formed in either a single step or two step process.

It will be understood that the methods, compositions, devices and embodiments described above are illustrative of the applications of the principles of the subject matter disclosed herein. It will also be understood that certain modifications may be made by those skilled in the art without departing from the spirit and scope of the subject mater disclosed and/or claimed herein. Thus, the scope of the invention is not limited to the above description, but is set forth in the following claims and/or any future claims made in any application that claims the benefit of this application. 

1. An orthopedic implant, comprising: an articulation portion having a pyrolytic carbon bearing surface; and a bone-fixation portion extending from the articulation portion and having a porous structure configured for bone on-growth or bone in-growth.
 2. The implant of claim 1 wherein the articulation portion further includes a substrate and the bone-fixation portion is bonded to the substrate.
 3. The implant of claim 2 further including a metal interlayer positioned at least partially between the bone-fixation portion and the substrate.
 4. The implant of claim 3 wherein the metal interlayer and the bone-fixation portion are comprised of the same metal material.
 5. The implant of claim 3 wherein the interlayer is comprised of a first metal and the bone fixation portion is comprised of a second metal, and the first metal is soluble with the second metal.
 6. The implant of claim 3 further including a metal outer layer at least partially covering the bone fixation portion and the interlayer, wherein the interlayer and metal outer layer bond the bone fixation portion to the substrate.
 7. The implant of claim 1 wherein the bone fixation portion is comprised of porous tantalum.
 8. The implant of claim 2 wherein the substrate is comprised of isotropic graphite.
 9. A method of forming an orthopedic implant, comprising: providing a carbon member having an articulation portion and a bone fixation portion with a porous region; applying a layer of pyrolytic carbon on an outer surface of the articulation portion; applying a metal coating to the porous region of the bone fixation portion.
 10. The method of claim 9 in which the metal coating is selected from the group consisting of tantalum, titanium, niobium or alloys or combinations thereof.
 11. The method of claim 9 wherein the pyrolytic carbon is applied by chemical vapor deposition.
 12. A method of forming an orthopedic implant, comprising: providing a substrate having a first surface and a second surface; applying a layer of pyrolytic carbon to the first surface of the substrate; placing an interlayer comprising a metal between the second surface of the substrate and a porous metal structure; and bonding the porous metal structure and the substrate together to form the orthopedic implant.
 13. The method of claim 12 wherein the bonding comprises applying heat and pressure to the substrate, interlayer and porous metal structure for sufficient time to achieve solid-state diffusion between the interlayer and the porous metal structure.
 14. The method of claim 12 wherein one of the porous metal structure and the interlayer is comprised of tantalum and the other is comprised of titanium.
 15. The method of claim 12 wherein the interlayer is applied to the second surface of the substrate by chemical vapor deposition.
 16. The method of claim 12 wherein the pyrolytic carbon is applied by chemical vapor deposition.
 17. A method of forming an orthopedic implant, comprising: applying a layer of pyrolytic carbon to a first surface of a substrate; applying a metal interlayer to a second surface of the substrate; contacting a porous metal structure with the metal interlayer; and applying a second outer layer of metal to the substrate, interlayer and porous metal structure.
 18. The method of claim 17 in which the metal interlayer, metal outer layer and porous metal structure all comprise the same metal.
 19. The method of claim 18 in which the metal is selected from the group consisting of titanium, tantalum, niobium or alloys or combination of the same.
 20. The method of claim 17 in which the pyrolytic carbon is applied to the substrate by chemical vapor deposition.
 21. The method of claim 17 in which the metal interlayer is applied to the substrate by chemical vapor deposition.
 22. The method of claim 17 in which the metal outer layer is applied by chemical vapor deposition.
 23. A method of forming an orthopedic implant, comprising: applying a layer of pyrolytic carbon to a first surface of a substrate; applying an interlayer comprised of a metal to a second surface of the substrate; providing a porous metal structure; placing a metal foil between the interlayer and the porous metal structure; and diffusion bonding the porous metal structure, the metal foil and the interlayer. 